Apparatus for x-ray generation and method of making same

ABSTRACT

A system for applying a target track material to an x-ray tube target includes a controller configured to direct a beam of energy toward an x-ray tube target, and direct a solid stock material toward the beam of energy to cause the solid stock material to melt and deposit as a melted material on the x-ray tube target.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of and claims priorityto U.S. patent application Ser. No. 11/865,928 filed Oct. 2, 2007, thedisclosure of which is incorporated herein.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to x-ray tubes and, moreparticularly, to a system for applying a target track material and amethod of fabrication.

X-ray systems typically include an x-ray tube, a detector, and a bearingassembly to support the x-ray tube and the detector. In operation, animaging table, on which an object is positioned, is located between thex-ray tube and the detector. The x-ray tube typically emits radiation,such as x-rays, toward the object. The radiation typically passesthrough the object on the imaging table and impinges on the detector. Asradiation passes through the object, internal structures of the objectcause spatial variances in the radiation received at the detector. Thedetector then emits data received, and the system translates theradiation variances into an image, which may be used to evaluate theinternal structure of the object. One skilled in the art will recognizethat the object may include, but is not limited to, a patient in amedical imaging procedure and an inanimate object as in, for instance, apackage in an x-ray scanner or computed tomography (CT) package scanner.

X-ray tubes include a rotating anode structure for the purpose ofdistributing the heat generated at a focal spot. The anode is typicallyrotated by an induction motor having a cylindrical rotor built into acantilevered axle that supports a disc-shaped anode target and an ironstator structure with copper windings that surrounds an elongated neckof the x-ray tube. The rotor of the rotating anode assembly is driven bythe stator. An x-ray tube cathode provides a focused electron beam thatis accelerated across a cathode-to-anode vacuum gap and produces x-raysupon impact with the anode. Because of the high temperatures generatedwhen the electron beam strikes the target, it is necessary to rotate theanode assembly at high rotational speed.

Newer generation x-ray tubes have increasing demands for providinghigher peak power. Higher peak power, though, results in higher peaktemperatures occurring in the target assembly, particularly at thetarget “track,” or the point of impact on the target. Thus, forincreased peak power applied, there are life and reliability issues withrespect to the target. Such effects may be countered to an extent by,for instance, spinning the target faster. However, doing so hasimplications to reliability and performance of other components withinthe x-ray tube. As a result there is greater emphasis in findingmaterial and fabrication solutions for improved performance and higherreliability of target structures within an x-ray tube. Furthermore,there is greater emphasis on repair and reuse of x-ray tube targets andother x-ray tube components. Thus there is a need to salvage what mightotherwise be unrecoverable x-ray tube targets.

Known deposition processes include plasma spray and powder applicationsintering methods such as laser-enhanced near-net shape (LENS). However,though such processes may be used to successfully deposit materials ofan x-ray tube target, such processes consume large volumes of expensivematerials such as tungsten, molybdenum, and the like and can result inmaterial waste. Further, such processes utilize a powder material whichmay limit available alloy options, and which typically precludes the useof tantalum and many Ta-alloys due to powder auto-inflammability.

Therefore, it would be desirable to have a method and apparatus toimprove target track fabrication and repair of an x-ray tube target.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention provide a method and apparatus thatovercome the aforementioned drawbacks. The x-ray target track isfabricated or repaired using a laser beam or other heating mechanism toheat the substrate of the target while applying a material to thesubstrate in order to fuse the materials together. The process may beperformed multiple times to form layered or graded structures orinterfaces, and it may be performed to fabricate complex geometries oftrack or substrate material on the surfaces of the target.

According to one aspect of the invention, a system for applying a targettrack material to an x-ray tube target includes a controller configuredto direct a beam of energy toward an x-ray tube target, and direct asolid stock material toward the beam of energy to cause the solid stockmaterial to melt and deposit as a melted material on the x-ray tubetarget.

According to another aspect of the invention, a method of fabricating anx-ray tube target includes directing a spatially coherentelectromagnetic beam toward a region of a target substrate, and feedinga solid stock material toward the region of the target substrate to meltthe solid stock material and form a first layer on the target substrate.

According to yet another aspect of the invention, a method of repairingan x-ray tube target includes pointing a laser beam toward a region ofan x-ray tube target to be repaired, such that the region is caused tomelt and form a melt region, and regulating a solid feedstock toward themelt region.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a block diagram of an imaging system that can benefit fromincorporation of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an x-ray tube useable with thesystem illustrated in FIG. 1 according to an embodiment of the presentinvention.

FIG. 3 is a flowchart of a target fabrication or repair processaccording to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of an x-ray tube target according to anembodiment of the present invention.

FIG. 5 is a pictorial view of a CT system for use with a non-invasivepackage inspection system.

FIG. 6 is a technique for fabrication of a new target and repair of anexisting target, according to embodiments of the invention.

FIG. 7 a system for applying a solid stock material to an x-ray tubetarget according to embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an embodiment of an imaging system 10designed both to acquire original image data and to process the imagedata for display and/or analysis in accordance with the presentinvention. It will be appreciated by those skilled in the art that thepresent invention is applicable to numerous medical imaging systemsimplementing an x-ray tube, such as a CT system, an x-ray system, avascular system, and a mammography system. Other imaging systems such ascomputed tomography systems and digital radiography systems also benefitfrom the present invention. The following discussion of x-ray system 10is merely an example of one such implementation and is not intended tobe limiting in terms of modality.

As shown in FIG. 1, x-ray system 10 includes an x-ray source 12configured to project a beam of x-rays 14 through an object 16. Object16 may include a human subject, pieces of baggage, or other objectsdesired to be scanned. X-ray source 12 may be a conventional x-ray tubeproducing x-rays having a spectrum of energies that range, typically,from 30 keV to 200 keV. The x-rays 14 pass through object 16 and, afterbeing attenuated by the object, impinge upon a detector 18. Eachdetector in detector 18 produces an electrical signal that representsthe intensity of an impinging x-ray beam, and hence the attenuated beam,as it passes through the object 16. In one embodiment, detector 18 is ascintillation based detector, however, it is also envisioned thatdirect-conversion type detectors (e.g., CZT detectors, etc.) may also beimplemented.

A processor 20 receives the signals from the detector 18 and generatesan image corresponding to the object 16 being scanned. A computer 22communicates with processor 20 to enable an operator, using operatorconsole 24, to control the scanning parameters and to view the generatedimage. That is, operator console 24 includes some form of operatorinterface, such as a keyboard, mouse, voice activated controller, or anyother suitable input apparatus that allows an operator to control thex-ray system 10 and view the reconstructed image or other data fromcomputer 22 on a display unit 26. Additionally, console 24 allows anoperator to store the generated image in a storage device 28 which mayinclude hard drives, floppy discs, compact discs, etc. The operator mayalso use console 24 to provide commands and instructions to computer 22for controlling a source controller 30 that provides power and timingsignals to x-ray source 12.

Moreover, the present invention will be described with respect to use inan x-ray tube. However, one skilled in the art will further appreciatethat the present invention is equally applicable for other systems thatrequire operation of a target used for the production of x-rays whereinhigh peak temperatures are driven by peak power requirements.

FIG. 2 illustrates a cross-sectional view of an x-ray tube 12 that canbenefit from incorporation of an embodiment of the present invention.The x-ray tube 12 includes a casing 50 having a radiation emissionpassage 52 formed therein. The casing 50 encloses a vacuum 54 and housesan anode 56, a bearing assembly 58, a cathode 60, and a rotor 62. X-rays14 are produced when high-speed electrons are suddenly decelerated whendirected from the cathode 60 to the anode 56 via a potential differencetherebetween of, for example, 60 thousand volts or more in the case ofCT applications. The electrons impact a material layer or target track86 at focal point 61 and x-rays 14 emit therefrom. The point of impactis typically referred to in the industry as the focal spot, which formsa circular region or track on the surface of the target track 86, and isvisually evident on the target surface after operation of the x-ray tube12. According to an embodiment of the present invention, target track 86may include a plurality of layers 92, 93, 94 applied according to thedisclosed process. The x-rays 15 emit through the radiation emissionpassage 52 toward a detector array, such as detector 18 of FIG. 1. Toavoid overheating the anode 56 from the electrons, the anode 56 isrotated at a high rate of speed about a centerline 64 at, for example,90-250 Hz.

The bearing assembly 58 includes a center shaft 66 attached to the rotor62 at first end 68 and attached to the anode 56 at second end 70. Afront inner race 72 and a rear inner race 74 rollingly engage aplurality of front balls 76 and a plurality of rear balls 78,respectively. Bearing assembly 58 also includes a front outer race 80and a rear outer race 82 configured to rollingly engage and position,respectively, the plurality of front balls 76 and the plurality of rearballs 78. Bearing assembly 58 includes a stem 83 which is supported bythe x-ray tube 12. A stator (not shown) is positioned radially externalto and drives the rotor 62, which rotationally drives anode 56. As shownin FIG. 2, a heat storage medium 90, such as graphite, may be used tosink and/or dissipate heat built-up near the target track 63.

Referring still to FIG. 2, the anode 56 includes a target substrate 84,having target track 86 attached thereto according to an embodiment ofthe present invention. The target track 86 typically includes tungstenor an alloy of tungsten such as tungsten with rhenium ranging from3-10%. The target substrate 84 typically includes molybdenum or an alloyof molybdenum such as TZM (Titanium, Zirconium, and Molybdenum).

According to embodiments of the present invention, the target track 86may be applied to a base substrate such as target substrate 84 by alaser consolidation process 96 as illustrated in FIG. 3. In process 96,the target substrate 84 is prepared at step 97, which may include, butis not limited to: 1) heat treatment such as may be required fordensification, stress relief, and the like; 2) surface preparation whichmay include cleaning, fusing, roughening, and the like; and 3) cleaningand mounting of the target substrate 84 in a fixture. At step 98, one ormore beams of laser energy are arranged to impinge an area of the targetsubstrate 84, thus heating a region of the target substrate 84. In oneembodiment of the present invention, the heating of the target substrate84 is adequate to melt a region of the target substrate 84. At step 99,powdered material is typically simultaneously supplied through a feederto the heated region of the target substrate 84 at a rate that iscontrolled so that the added material melts and bonds with theunderlying material of the target substrate 84. At step 100, afterapplication of a layer, it is determined whether another layer isdesired and, if so, the process at 101 repeats steps 97, 98 and 99,which may include changing the material of the powder to be applied asdescribed above. If no further layers are desired, then at step 102, theprocess calls for moving to a post-processing step at 103, during whichthe target may be removed, cleaned, and otherwise prepared for furtherassembly with anode 56. The target track 86 typically may range fromthicknesses ranging from tens of microns in thickness to hundreds ofmicrons in thickness.

Referring now to FIG. 4, a multi-layer target track 86 may be applied tothe target substrate 84 according to an embodiment of the presentinvention employing process 96 as described in FIG. 3. A first layer 92is applied to the target substrate 84 as described above. Then, eachsucceeding layer 93, 94 is applied on preceding layers 92, 93,respectively, one at a time as described above such that layers 92, 93serve as base substrates for layers 93, 94, respectively. In oneembodiment, layer 92 is tungsten, layer 93 is rhenium, and layer 94 isan alloy of tungsten and rhenium. It is recognized that target track 86may include more or less than three layers, or that the layers 92-94 mayinclude combinations and alloys thereof. It is further recognized thatthe layers 92-94 may be applied with materials that may include powdersthat contains a mix of alloying components. As an example, layer 92, forinstance, may be applied using a powder having 5% rhenium and in amixture. As such, layer 92 may be applied as an alloy that will formupon impingement with the heated region on the target substrate 98.

Process 96 may be altered from that described above, according toembodiments of the present invention, to use other materials such asrhodium and its alloys, alloys of tungsten, alloys of molybdenum, alloysof tantalum, alloys of rhenium, and other refractory and non-refractorymetals. For instance, one skilled in the art will recognize thatspecific properties of the target track 86 may be affected according tothe thicknesses of individual layers 92-94 applied to the substrate 84,how many layers 92-94 are applied overall, and the selection ofmaterials and their mixtures during process 96 at step 99. Materialproperties that may be affected by appropriate selection of process 96parameters include but are not limited to surface emissivity,coefficient of thermal expansion (CTE), thermal conductivity, fatiguestrength and crack resistance, and elastic modulus. For instance, oneskilled in the art will recognize that tantalum, having a relativelyhigh CTE and a relatively low elastic modulus as compared generally toother metals, may be applied as one or more layers to affect the overallCTE and elastic modulus of target track 86. Furthermore, such materialsmay not be limited to use as x-ray emission materials, but may also beapplied according to an embodiment of this invention as braze materialsincluding, but not limited to, zirconium, titanium, vanadium, andplatinum. Such materials may also be used for surface emissivityenhancement. Additionally, one skilled in the art would recognize thatlayers of materials 92, 94, 96 may be applied to the target substrate 84to protrude or extend from a surface of the substrate 84.

One skilled in the art will further recognize that many combinations ofmaterials may be applied in powder form at step 99 of process 96. Forinstance, a gradient of materials may be applied to fabricate targettrack 86 by applying, for instance, first layer 92 having 75% tungstenand 25% rhenium, and second layer 93 having 90% tungsten and 10%rhenium. As such, target track 86 may be formed having a gradient, orvarying concentration of elements, therein, by appropriately selectingand varying the alloying elements from one layer to the next.

Materials applied using the process described herein need not be limitedto those described above. One skilled in the art will recognize that, inaddition to metals, oxides, including but not limited to oxides oflanthanum, yttrium, aluminum, and zirconium, may be applied according toembodiments of the present invention. Furthermore, carbides, includingbut not limited to carbides of titanium, hafnium, and boron, may beapplied as well.

The process 96 disclosed herein can likewise be performed on pre-formedtarget cap materials. Accordingly, the materials deposited thereon mayinclude wrought materials as well. Additionally, the process describedherein allows the deposition of graded structures of track material, aswell as complex geometries.

The process described herein need not be limited to new x-ray targetfabrication, but may be applicable to repair and reuse of targets aswell. Accordingly, targets may be salvageable by disassembling them fromthe x-ray tube and reprocessing them by using the method describedherein. Targets having track material 86 damaged after use may berecovered by having the target track 86 replaced or repaired.Additionally, new targets fabricated with defects that may include butare not limited to pits, cracks, and voids may be recoverable via thismethod as well. As such, target preparation step 97 of process 96 mayinclude but is not limited to target disassembly from an anode 56, andmachining or grinding of the target track 86 to expose the substrate 84prior to applying a first layer 92.

High-density coatings may be fabricated with this method as well.Density problems inherent in, for instance, a plasma-spray process maybe mitigated by use of this process to apply high-density coatings toincrease mechanical properties such as spallation and fatigueresistance. For some materials and material combinations,post-processing including but not limited to hot isostatic pressing(HIP) processing may be required.

Referring now to FIG. 5, package/baggage inspection system 510 includesa rotatable gantry 512 having an opening 514 therein through whichpackages or pieces of baggage may pass. The rotatable gantry 512 housesan x-ray energy source 516 as well as a detector assembly 518 havingscintillator arrays comprised of scintillator cells similar to thatshown in FIG. 4 or 5. A conveyor system 520 is also provided andincludes a conveyor belt 522 supported by structure 524 to automaticallyand continuously pass packages or baggage pieces 526 through opening 514to be scanned. Objects 526 are fed through opening 514 by conveyor belt522, imaging data is then acquired, and the conveyor belt 522 removesthe packages 526 from opening 514 in a controlled and continuous manner.As a result, postal inspectors, baggage handlers, and other securitypersonnel may non-invasively inspect the contents of packages 526 forexplosives, knives, guns, contraband, etc.

Referring now to FIG. 6, a technique 600 is illustrated that includesfabrication of a new target and repair of an existing target, accordingto embodiments of the invention. Technique 600 begins at step 602, andat step 604, a target is obtained. In one embodiment of the invention,the target obtained may be a new target substrate that is prepared andready for a target track to be applied thereto, according to embodimentsof the invention. In another embodiment, despite being a new target thatmay already have its track applied thereto, it may be determined thataspects of the target need re-work or repair prior to use, such as whena target has a surface specification (such as a flatness) that is out ofspecification. Conversely, the target obtained may be a used target inneed of having a track repaired or re-worked, according to anotherembodiment of the invention. In some instances, either for a new targetor for a target repair, it may be desirable to machine the target priorto applying a layer or repairing a track. Thus, at step 606, if thetarget is to be machined 608, then a surface of the target is machinedat step 610.

Whether machined at step 610 or not 612, the target is positioned in aholder at step 614. At step 616 it is determined whether to pre-heat thetarget. If so 618, then at step 620 the target is pre-heated. And,whether pre-heated or not 622, energy may be directed toward the targetat step 624. In embodiments of the invention, the energy directed towardthe target at step 624 includes a beam of laser energy or a spatiallycoherent electromagnetic beam. However, the invention is not to be solimited, and is applicable to use of any heating method where a surfacemay be selectively heated, to include induction heating, electron-beamheating, and focused infrared heating, as examples. Thus, although alaser beam may be described for the purpose of heating a surface, it isto be understood that any heating method, as described, may likewise beused within the scope of the invention.

In embodiments of the invention, the holder is placed in an atmosphereconducive to laser cladding and LENS deposition including an atmospherethat prevents substantial surface reaction of the substrate withconstituents present within the atmosphere. High vacuum and inert gasesare effective in prohibiting these interactions. Reducing gases such ashydrogen or carbon monoxide are typically effective in preventingoxidation. As understood within the art, depending on substratecomposition, the atmosphere should be free of some constituents. Forexample, the atmosphere should be free of sulfur to avoid the formationof silver sulfide (aka tarnish), or free of nitrogen to avoid theformation of titanium nitride.

In embodiments of the invention, the holder is a moveable holder, andthe target may be moved while directing the laser thereto. In otherembodiments of the invention, the target is maintained in a stationaryposition with respect to the laser beam in order that a single spot maybe repaired or have material applied thereto. In other embodiments ofthe invention, both the laser and wirefeed are moveable such that thetarget may be either stationary or moveable, and the laser/wirefeed maybe moveable with respect to the target in order to apply spot repair ora full layer thereto.

For instance, in one example, when the target is positioned in theholder at step 614, the holder is a stationary holder that may beclamped and held in position while the laser beam and solid stockmaterial are applied thereto. In such an example, a limited region orspot of material may be applied to the material, and the target may bemanually repositioned in order to apply the material in limited portionsof the target. In another example, when the target is positioned in theholder at step 614, the holder is a moveable holder that may be used tocause the target to move while the laser and the solid stock materialare applied thereto, as described above. In one embodiment, the moveableholder is a turntable that may be used to direct the laser beam andsolid stock material to a fixed radial location with respect to thetarget such that a circumferentially directed cladded layer of materialmay be applied to the target.

At step 626, one or more solid stocks of material are directed towardthe target, according to embodiments of the invention. In embodiments,the solid stock of material is a thin wire stock (sub-millimeter to afew millimeters in diameter), a narrow strip stock (a few millimeterswidth or less), a thick wire stock (a few millimeters and greater indiameter), and the like. In one embodiment, the solid stock of materialis a wide strip stock that is a few millimeters in width or greater. Inembodiments of the invention, the solid stock material is molybdenum oralloys thereof, tungsten or alloys thereof (e.g., with rhenium), andtantalum or alloys thereof. In one example, an alloy of tungsten,rhenium, and tantalum is used. In one embodiment of the invention thesolid stock or wirefed material is optionally heated by a heater in situto a temperature below its melt temperature and prior to entering thebeam. Thus, in this embodiment, because the solid stock is pre-heated,there is therefore less heating applied to the target in order to meltthe solid stock material. As such, thermally induced distortion of thetarget may be reduced when applying a spot or material layer thereto.

In directing the solid stock of material toward the target at step 626,a spot or layer of material may be melted and formed on the target,according to embodiments of the invention. In one embodiment, the laseris directed toward a target surface, thereby causing the target to melt.In this embodiment, the solid stock is directed into the melted targetmaterial and the solid stock, in turn, melts and mixes with the meltedtarget material. In another embodiment, the laser is directed toward thetarget, but the solid stock of material is directed into a path of thelaser, causing the solid stock of material to melt and form on thetarget. In still another embodiment, the laser is directed toward thetarget, and the solid stock of material is simultaneously applied to alocation where the laser impinges on the target, causing both the targetand the solid stock of material to melt and mix. In yet anotherembodiment, in an instance where a wide strip stock solid material isused to add material to a target, it is possible to raster the laserbeam in a direction that is transverse to a direction of a portion ofthe target where the laser beam is applied in order to heat and melt aregion of the target and the wide stock material that is significantlywider than the laser beam. Further, instead of rastering the laser beam,embodiments of the invention also include moving the target with respectto the beam, in which case a stationary beam may be rastered by insteadmoving the target. In examples, an articulated robot or robotic arm maybe used to move the beam with respect to the target, or the target withrespect to the beam. In an alternate embodiment, instead of rasteringthe beam to heat and/or melt a wide strip solid stock material, a lineshape diode source may be instead used to heat the wide strip. In otherwords, a plurality of heating sources, such as to form a line shapediode source, may be used to cause heating and melting of the wide stripsolid stock material.

Thus, embodiments of the invention include multiple techniques forapplying a solid stock of material to a target surface via a laser, andone skilled in the art will recognize that techniques may be developedfor applying the combination of a laser beam or other heating method,and a solid stock of material, in order to apply a material or layer toa target. Such techniques are included within the scope of thisinvention.

At step 628, it is determined whether an additional layer or spot ofmaterial is desired to be applied to the target. If so 630, thentechnique 600 next determines at step 631 whether to machine, grind,clean, stress relieve, and/or otherwise work the surface of theadditional layer or spot. If so 635, then the surface of the target ismachined and/or cleaned and/or stress relieved at step 637 and controlreturns to step 624 such that material may again be applied. If not 639,then control returns to step 624 with no machining, cleaning, or stressrelieving between layers. When control returns to step 624, a laser beamis again directed toward the target. In this example, the target may bere-positioned in the holder in order that the laser beam may be directedtoward another spot on the target, or toward a different circumferentiallocation of the target. If no additional layer or spot of material isdesired to be applied to the target 632, then it is next determined atstep 634 whether to clean up the surface of the target and/or stressrelieve the target prior to use. If so 636, then surfaces of the targetmay be machined and/or stress relieved at step 638, and technique 600ends at step 640. If no surface cleanup is desired or necessary 642,then technique 600 ends at step 644.

Thus, in embodiments of the invention, a balance mark, anout-of-tolerance region, a focal track erosion region, and a focal trackcrack region may be repaired. Embodiments of the invention also includeenabling grading a target substrate and layering chemistries of the sameor differing materials thereon. Further, embodiments of the inventioninclude enabling the use of wrought materials for substrates. Thus,laser cladding and LENS deposition enable the incorporation of solidsubstrate preforms, meaning that it enables an alternative to typicalco-pressing (and ensuing co-processing requirements) of substrate powderand layer powder. By depositing layers onto a solid substrate,additional material choices are enabled, including both materialcompositions and degrees of material processing. Wrought (i.e.,mechanically worked) material offers key advantages in unique instances,such as with ODS-Mo (oxide dispersion strengthened molybdenum alloy)wherein mechanical working results in a refined dispersion strengthenedmicrostructure that possesses great advantages in re-crystallizationtemperature and creep resistance (among others).

FIG. 7 illustrates a system or apparatus 700 for applying a solid stockmaterial 702 to an x-ray tube target 704, according to embodiments ofthe invention. As illustrated, system 700 includes a holder 706 on whichtarget 704 is positioned. Holder 706 may be configured to linearlytranslate 708 target 704, or holder 706 may be configured to rotate 710target 704 about a rotational center 712 such that a cladded layer 714may be deposited and formed thereon at a radial distance 716 fromrotational center 712. System 700 includes an ability to apply a laserbeam or a spatially coherent electromagnetic beam 718 to a surface 720of target 704, according to embodiments of the invention. Further, it isto be understood that the invention is not limited to application of alaser beam or a spatially coherent electromagnetic beam, and thatsurface 720 of target 704 may likewise be heated using any heatingmethod, and that beam 718 may represent induction heating, anelectron-beam, and a focused infrared beam, as examples.

As stated with respect to technique 600 above, embodiments of theinvention include directing a laser toward the target surface 720, inwhich case the solid stock material 702 is directed into melted targetmaterial and the solid stock material 702, in turn, melts and mixes withthe melted target material. Embodiments also include directing laserbeam 718 toward target 704 but solid stock of material 702 is directedinto a path of the laser beam 718, causing solid stock of material 702to melt and form on target 704. Another embodiment includes directinglaser beam 718 toward target 704 and solid stock of material 702 issimultaneously applied to a location 722 where laser beam 718 impingeson target 704, causing both target 704 and solid stock of material 702to melt and mix. In the embodiment where a wide strip stock solidmaterial 702 is used to add material to target 704, it is possible toraster or rapidly alternate laser beam 718 back and forth in a direction724 that is transverse to direction 708, in order to heat and melt aregion of target 704 and stock material 702 that is significantly widerthan laser beam 718.

System 700 includes a controller 726 having one or more control lines728, and controller 726 is configured to control operational aspects ofsystem 700. In embodiments of the invention that include pre-heating thetarget, system 700 includes a heater 730 that may be used to heat orpre-heat target 704. Further, one skilled in the art will recognize thatheater 730 need not be part of system 700 that is controlled bycontroller 726, but that heater 730 may be a device that is entirelyseparate of system 700 and separately controlled. One skilled in the artwill also recognize that the heater may be used to heat only x-ray tubetarget 704, or it may be used to heat x-ray tube target 704 after it hasbeen placed in holder 706.

Thus, according to the invention and as understood in the art,controller 726 is configured to control either a linear translationrate, distance traveled, timing, etc. of holder 706 along linear path708 (in an embodiment that includes linear travel), and controller 726is configured to rotate holder 706 about rotational axis 710 at adesired rotational rate (in an embodiment that includes rotationaltravel), as examples. Controller 726 is also able to control otheraspects of system 700 such as a feed rate of material 702, power andlocation of laser beam 718, heater 730, and the like. Thus, embodimentsof the invention include system 700 having a controller 726 forcontrolling application of a solid stock of material to a target surfacevia a laser.

A technical contribution for the disclosed method and apparatus is thatit provides for a system for applying a target track material and amethod of fabrication.

According to one embodiment of the invention, a system for applying atarget track material to an x-ray tube target includes a controllerconfigured to direct a beam of energy toward an x-ray tube target, anddirect a solid stock material toward the beam of energy to cause thesolid stock material to melt and deposit as a melted material on thex-ray tube target.

According to another embodiment of the invention, a method offabricating an x-ray tube target includes directing a spatially coherentelectromagnetic beam toward a region of a target substrate, and feedinga metallic stock material toward the region of the target substrate tomelt the metallic stock material and form a first layer on the targetsubstrate.

According to yet another embodiment of the invention, a method ofrepairing an x-ray tube target includes pointing a laser beam toward aregion of an x-ray tube target to be repaired, such that the region iscaused to melt and form a melt region, and regulating a solid feedstocktoward the melt region.

Embodiments of the invention have been described in terms of thepreferred embodiment, and it is recognized that equivalents,alternatives, and modifications, aside from those expressly stated, arepossible and within the scope of the appending claims.

What is claimed is:
 1. A system for applying a target track material to an x-ray tube target, the system comprising a controller configured to: direct a beam of energy onto an x-ray tube target; and direct a solid stock material toward the beam of energy to cause the solid stock material to melt and deposit as a layer of melted material on the x-ray tube target, wherein the solid stock material has a width that is greater than a width of the beam of energy.
 2. The system of claim 1 wherein the beam of energy is one of a laser beam, an electron-beam, a focused infrared beam, and energy from an induction heater.
 3. The system of claim 1 wherein the controller is configured to move a portion of the x-ray tube target in a first direction relative to the beam of energy while directing the beam of energy toward the x-ray tube target and while directing the solid stock material toward the beam of energy.
 4. The system of claim 3 wherein the controller is configured to raster the beam of energy in a second direction that is transverse to the first direction.
 5. The system of claim 1 wherein the controller is configured to direct the beam of energy into the x-ray tube target to form an x-ray tube target melt pool, and direct the solid stock material into the x-ray tube target melt pool to cause the solid stock material to melt.
 6. The system of claim 1 wherein the controller is configured to simultaneously direct the beam into the x-ray tube target and direct the solid stock material into the beam to cause the solid stock material to melt.
 7. The system of claim 1 wherein the controller is configured to direct power to a heater to pre-heat the target prior to directing the beam of energy toward the target.
 8. The system of claim 1 wherein the controller, in being configured to direct a solid stock material, is configured to direct one of a wire, a strip, and a rod toward the locally melted location.
 9. A method of fabricating an x-ray tube target, the method comprising: directing a spatially coherent electromagnetic beam onto a region of a target substrate; and feeding a solid stock material toward the region of the target substrate to melt the solid stock material and form a first layer of material from the solid stock material on the target substrate, wherein the solid stock material has a width that is greater than the spatially coherent electromagnetic beam.
 10. The method of claim 9 further comprising pre-heating the target substrate prior to directing the spatially coherent electromagnetic beam toward the region of the target substrate.
 11. The method of claim 9 further comprising moving a portion of the target substrate in a first linear direction with respect to the spatially coherent electromagnetic beam.
 12. The method of claim 9 wherein feeding the solid stock material comprises feeding one of molybdenum, an alloy of molybdenum, tungsten, an alloy of tungsten, tantalum, and an alloy of tantalum.
 13. A method of repairing an x-ray tube target, the method comprising: applying a laser beam to a region of an x-ray tube target to be repaired, such that the region is caused to melt and form a melt region; and regulating a solid feedstock toward the melt region to cause the solid feedstock to melt in the melt region and deposit molten solid feedstock material on the x-ray tube target, wherein regulating the solid feedstock toward the melt region comprises regulating the solid feedstock having a width that is greater than that of the laser beam.
 14. The method of claim 13 further comprising identifying a region of the x-ray tube target to repair prior to pointing the laser beam toward the region, the region comprising one of a balance mark, an out-of-tolerance region, a focal track erosion region, and a focal track crack region.
 15. The method of claim 13 further comprising heating the target substrate prior to pointing the laser beam toward the region of the x-ray tube target to be repaired.
 16. The method of claim 13 further comprising displacing the x-ray tube target in a linear direction while pointing the laser beam toward the region of the x-ray tube target to be repaired.
 17. The method of claim 13 wherein the solid feedstock is one of a wire, a strip, and a rod.
 18. The system of claim 1 wherein the controller is configured to heat the solid stock material to a temperature below its melt temperature prior to directing the solid stock material toward the beam of energy.
 19. The method of claim 9 comprising heating the solid stock material to a temperature below its melt temperature prior to feeding the solid stock material toward the region of the target substrate.
 20. The method of claim 13 comprising heating the solid feedstock prior to regulating the solid feedstock toward the melt region. 